NudgingSteel wrote
...having worked at several airports in my career I can tell you that I have never been involved in turning light a/c away or worrying about whatever handling fees they're going to get charged.
But it definitely does happen at some airports. ATC at Southampton have to get involved when an inbound GA has no PPR. This is normally a simple case of getting them to call the handling agents but it all takes time explaining that PPR is required and giving the handling frequency etc. Sometimes the agents allow them in on certain conditions (e.g ok if only staying a short time) but at other times they turn them away if for example there is no parking space. Once refused, ATC then get involved again either by finding out if Bournemouth will accept them (also PPR) or by suggesting other alternatives. As NudgingSteel says it is not an ATC decision and although they always strive to be as helpful as possible I'm sure they could do without this extra workload at busy times.